1. Field of the Invention
The present invention relates to an electrophotographic apparatus which forms an image on a recording member by using the electrophotographic process.
2. Description of the Related Art
In the electrophotographic process, it is known that a corona discharger comprising a corona discharge wire is used as transferring means for transferring a toner image formed on an image carrier such as a photosensitive member to a recording member such as a paper sheet.
A transfer corona discharger (hereinafter, referred to as xe2x80x9ca transferring devicexe2x80x9d) supplies charges of a polarity opposite to that of a toner, to the rear face of a recording member, i.e., the face opposite to the face to which a toner image is to be transferred, thereby transferring the toner image on the image carrier onto the recording member.
The recording member which has received the toner image from the image carrier must be then transported to a fixing device so that the toner image is fixed to the recording member. However, it is often that, after the transferring step, the recording member is caused by the influence of an electrostatic force not to be successfully separated from the image carrier, with the result that the recording member is wound around the image carrier.
In order to prevent such a failure of separation of a recording member from an image carrier from occurring, a countermeasure is usually taken on an electrophotographic apparatus of this kind in the following manner. A separation corona discharger (hereinafter, referred to as xe2x80x9ca separating devicexe2x80x9d) is disposed in a stage subsequent to the transferring device. When, for example, positive charges are supplied from the transferring device to the rear face of a recording member, the separating device supplies negative charges to the rear face of the recording member to neutralize electrostatic charges on the recording member, so that the recording member can be smoothly transported toward the fixing device without being wound around the image carrier.
However, it is known that the flow-in currents to a recording member from the transferring device and the separating device are varied depending on the kind and ream weight of a recording member which is used in printing, or environmental conditions (the percentage of water absorption of the recording member, the environment at the periphery of a corona discharge wire, and the like). Under given preset conditions, it is difficult to realize stable transfer/sepration.
For example, Japanese Patent Laid-Open No. 160125/1995 proposes a configuration in which the temperature and humidity at the periphery of a corona discharge wire of a separating device are detected, and the discharge voltage of the corona discharge wire of the separating device is changed on the basis of a result of the detection, thereby realizing stable transportation of a recording member.
In the configuration disclosed in Japanese Patent Laid-Open No. 160125/1995, a countermeasure against deterioration with age of a corona discharge wire is not taken, and hence further room remains for improvement.
It is an object of the invention to provide an electrophotographic apparatus in which, irrespective of deterioration of a corona discharge wire, stable separation and transportation of a recording member can be realized for a long term.
The object is realized by an electrophotographic apparatus comprising: a transferring device which is configured by a corona discharger comprising: a shielding section that has an aperture in a part; and a corona discharge wire that is supported by the shielding section, the transferring device transferring a toner image formed on an image carrier to a recording member; and a separating device which is configured by a corona discharger comprising: a shielding section that has an aperture in a part; and a corona discharge wire that is supported by the shielding section, the separating device being disposed downstream in a recording member transporting direction from the transferring device, and releasing charges of a polarity opposite to a polarity of charges released from the transferring device, wherein a transfer flow-in current which flows from the transferring device into the image carrier, a separation flow-in current which flows from the separating device into the image carrier, an aperture width in the recording member transporting direction of the aperture of the transferring device, and an aperture width in the recording member transporting direction of the aperture of the separating device are set to have a following relationship: separation flow-in current=transfer flow-in currentxc3x97(transfer aperture width/separation aperture width).